The virtual bridged local area networks (VLAN) 802.1Q protocol defines bridge rules for cross-switch communications of a same VLAN and frame formats for proper identifying VLAN, a 12-bit VLAN Tag of a data frame is used to identify the VLAN that a host locates. Due to that the VLAN Tag has only 12 bits, an apparatus can support at most 4094 VLANs. A data frame of a same VLAN, which may be a unicast frame, a multicast frame or a broadcast frame, is limited to be transmitted in the VLAN. In real applications, especially in Metropolitan Area Networks, a lot of VLANs are required to isolate users; and 4094 VLANs are far from meeting the requirements. QinQ (802.1Q in 802.1Q), also named as stacked VLAN or double VLAN technology, is a technology for expanding the VLAN space, and is implemented by encapsulating another layer of virtual bridged local area network protocol tag once again before a layer of virtual bridged local area network protocol tag. A layer of private network VLAN Tag is used to identify a customer network, a layer of public network (backbone network) VLAN Tag is used to identify a carrier network (Provider Network), and the private network VLAN Tag is encapsulated in the public network VLAN Tag, so that a message carries two layers of VLAN Tags to traverse the public network (backbone network). In the public network, an apparatus forwards the message only according to a public network VLAN Tag in an outer layer, and the private network VLAN Tag is transmitted as a data part of the message.
To transmit IP (Internet Protocol) data message on a physical link, it is needed to obtain a destination physical address according to a destination IP address, by neighbor detection. For example, the destination physical address is obtained by using ARP (Address Resolution Protocol) or ND (Neighbor Discovery) protocol. However, when neighbor detection is performed on a QinQ termination interface, as the VLAN will divide a broadcast domain, it is needed to send a detection message to traverse the public network VLAN and the private network VLAN, until a target terminal is found. Since performing neighbor detection by traversing the public network VLAN and the private network VLAN will produce numerous invalid detections, the apparatus load is increased and a lot of processor (such as CPU) resources are consumed.